1. Field of the Invention
The present invention relates to a fabrication method of nano-crystals, and more particularly, to a fabrication method of nano-crystals serving as a coulomb island at the room temperature using a focused-ion beam (FIB).
2. Description of the Related Art
In the fabrication of a single electron tunneling transistor (SET) or a quantum device for a next generation-high memory integrated circuit, it is a problem of great urgency and essentiality to form nano-crystals for electron binding. In order for the nano-crystals to bind tunnel electrons at room temperature, sizes of the nano-crystals for binding the electrons should be a few ten nm or less such that the nano-crystals have a binding force of greater than the thermal fluctuation energy of the electrons at the room temperature.
At the present, there is mostly being used a growing method in order to form the nano-crystals or quantum island. However, there are several problems in applying this growing method to a real process because of a complicated process and a difficult control of the growing method.
In the meanwhile, a focused-ion beam system is a system used in repairing an integrated circuit or a maskless lithography and its technical development reaches a level capable of directly processing an ultra fine structure of a unit of micron (xcexcm) or less based on the development of liquid metal ion source.
However, there is not yet any try to form the nano-crystals using the focused-ion beam technology.
Accordingly, it is an object of the present invention to provide a method for fabricating nano-crystals serving as coulomb island at room temperature using a focused-ion beam.
To accomplish the above object and other advantages, there is provided a method for forming a nano-crystal. In the above method, there is prepared a substrate having a metal film or a semiconductor film formed thereon. A focused-ion beam is irradiated onto a plurality of positions on a surface of the metal film or the semiconductor film, whereby the metal film or the semiconductor film is removed at a focal portion of the focused-ion beam but an atomic bond in the metal film or the semiconductor film is broken at an overlapping region of the focused-ion beams due to an radiation effect of the focused-ion beam to form the nano-crystal.